Motor lubricating oils and methods for using same



MOTOR LUBRICATING OILS AND METHODS FOR USING SAME Harry W. Rude], Roselle, and Victor F. Massa, Union, NJ., assignors to Esso Research and Engineering Com- The present invention relates to improved lubricating oils for use in internal gasoline combustion engines of the reciprocating type. The invention is also concerned with methods for operating high compression ratio automotive engines and the like with the improved lubricating oils of the present invention in combination with essentially hydrocarbon gasoline fuels containing harmful sulfur compound impurities. In essence, the improved motor oil compositions of the present invention include relatively high-boiling, halogenated hydrocarbons in small amounts effective for combating octane requirement increase in internal combustion engines.

During recent years, the introduction and widespread use of motor vehicles having high compression ratio engines has emphasized problems of power loss and fuel octane requirement increase of the engine as a result of combustion chamber deposit accumulation. posits, to the formation of which both the hydrocarbon fuel and the crankcase lubricant contribute, contain carbon, hydrogen, oxygen, sulfur and nitrogen in the organic portion. When a gasoline containing tetraethyl lead (TEL) and halide scavengers for the TEL is used, lead compounds (oxides, chlorides, sulfates, etc.) are present in the deposits. Such deposits also contain resin-like materials that have poor heat conductivity and insulate the walls of the combustion chamber. This leads to knocking, preignition and power loss difficulties, raises the octane requirement of engine by as much as 10 to 15 units during the first few thousandmiles of operation, and causes other difficulties.

In copending U.S. patent applications, Serial Nos. 375,137, now Patent No. 2,849,398, 375,138 and 375,158, both now abandoned, tiled in the names of Leonard E. Moody and Alexander H. Popkin on August 19, 1953, the disclosures of which are incorporated herein by reference, various means for combating octane requirement increase (ORI) in such engines are taught, with special emphasis being placed on non-ORI coutributing lubricating oil compositions and on methods for operating engines lubricated with these oils in conjunction with fuels having special characteristics. Their work showed that compounded motor lubricants having a low resinification index, i.e., a reduced tendency to form resin-like deposits during combustion under a cleanburning flame such as that produced by a hydrogen flame, do not contribute substantially to ORI, and that to obtain substantial advantages from the improved oil requires the use of a fuel not having substantial tendency to contribute to ORI. For example, they found that TEL-containing fuels will act in several ways. If the fuel contains less than about 0.01% sulfur, the TEL fluid leaves deposits that seem to have an anti-knock effect. If. substantially more sulfur is present in the fuel, lead sulfate and possibly other lead salts are formed that remain in the deposits and contribute to ORI.

Although complete elimination of TEL from sulfurcontaining fuels or the elimination of sulfur fromTEL- ".containing fuels would substantially prevent this sulfur- Such de-' lubricants and fuels.

2,942,588 Patented June, 28, 1960 lead interaction and the harmful effects thereof, such a solution is generally impractical from an economic point of view. Most motor fuels comprise straight run and catalytically cracked naphthas containing sulfur compounds. Treating such fuel components to reduce sul-' fur in the. fuel to much below 0.05% is still not commercially feasible.- TEL fluid is still neededin gasoline to boost the octane number to levels needed for modern high compression engines (such as 7:1 compression ratios and higher).

The aforesaid Moody et al. applications teach the use of high-boiling halogenated hydrocarbons, such as bromoxylene as lead scavenging agents in leaded, sulfurcontaining fuels for use in conjunction with low-resinification index motor lubricants. Such high boiling lead scavenging agents have been shown to be superior to the conventional ethylene chloride-ethylene bromide types normally present in TEL fluid, but complete elimination of the ORI difficulty is not always obtained; The degree of improvement to be obtained appears to vary considerably depending on the type of engine and conditions of engine operation, as well as upon the fuel and motor oil compositions used. It would therefore be desirable to find a means of utilizing leaded, sulfur-containing hydrocarbon fuels that more consistently eliminate the harmful effects of the lead-sulfur interaction. It is therefore a principal object of the present invention to teach improved motor lubricant compositions that have increased effectiveness in combating the tendency of octane requirement increase in high compression ratio engines caused by the formation of poor heat conductivity deposits in the combustion chamber. further object to teach methods of operating such engines with gasolines containing tetraethyl lead anti-detonant and sulfur compound impurities whereby maximum advantage can be taken of improved lubricating oils.

In accordance with the present invention, a lubricating oil is formulated to contain a minor amount of a relatively high boiling, halogenated hydrocarbon, preferably 'of an internal combustion chamber'subject to friction,

is used to lubricate the combustion chamber in conjunction with an essentially hydrocarbon motor fuel that contains tetraethyl lead and 'sulfur' compound impurities. The motor fuel may also contain a lead scavenging agent of the conventional, relatively volatile types, such as the low-boiling halogenated hydrocarbons, or of the-relatively high-boiling halogenatedhydrocarbons such as those employed in the lubricating oils of the present invention. By'operating the engine in this manner, the tendency of harmful combustion chamber deposits that contribute to octane requirement increase is "substantially retarded, and more effective engineoperation is realized than is realized in the case when employingconvent'ion'al The theoretical basis for the improvements obtained in the practice of the invention are not fully understood at the present, but possible mechanisms havebeen'formw lated that probably account, at leastin part, for,the'i'm provements realized. Without wishing to be bound by such theoretical considerations, it is postulated that the incorporation of the high-boiling halogenated hydrocarbon in the lubricating oil performs its desirable function Itisa action.

by carrying the halogenated material to the surface of the combustion zone on which the deposits accumulate. In this manner, it can react with the lead compounds that form on the combustion chamber surface and therefore tend either to prevent or retard the harmful lead-sulfur interaction from taking place or to mitigate the harmful effects of any such interaction that occurs. It is possible that the high boiling scavenging agents in the fuel do not always perform their intended function because they may be completely burned in the combustion zone proper before having an opportunity to contact the combustion zone surfaces. The lubricating oil, on the other hand, is not introduced into the combustion zone in vaporized form and is able to contact the critical surfaces before all of the halogenated hydrocarbon contained therein is decomposed. This, in effect, leads to more consistent performance in preventing the lead-sulfur inter- Since most lubricating oils, particularly of the mineral-base type, contain sulfur compounds, this also provides a means of resisting of the formation of harmful deposits by a lead-sulfur interaction between the tetraethyl lead and the sulfur in the oil.

The invention will now be explained in more detail in connection with the following specific example.

A mineral oil base stock is obtained by solvent extracting and dewaxing a Mid-Continent distillate. This base stock has a boiling range of about 325 to 500 F. at 10 mm. Hg pressure absolute in an Engler distillation,

0.08 weight percent sulfur, 37 API gravity, S.U.S. viscosities at 100 and 210 F. of 66 and 36, respectively, and a resinification index, as determined by the procedure described in the aforesaid Moody et al. applications, of about 4.0 mg./5 grams.

A suitable oil composition contains 83.3% of this base stock; of a viscosity index improver and thickener consisting of an oil solution of polyisobutylene having an average molecular weight of about 15,000; 5% of a commercial detergent additive, 0.2% of P S -treatcd alpha pinene, 0.5% of zinc dialkyl dithiophosphate and 1.0% of mixed mono-bromoxylenes having a vapor pressure at 120 F. of about 2 mm. Hg.

This oil is used as a crank case lubricant in an eightcylinder automobile having a compression ratio of about 7.5:1. The automobile is operated with a fuel consisting chiefly of isopentane and catalytic and virgin naphthas. The fuel has an API gravity of 63, a research octane number of 90, 0.06% sulfur,.41% olefins and 9% aromatics. To the fuel is added 2 cc. TEL/gallon and 1.5 stoichiometrical equivalents, based on the amount required to form lead halides with the -TEL, of an ethylene bromideethylene chloride scavenging agent.

The automobile is operated using this motor oil and fuel combination whereby substantially reduced ORI, resultingfrom lead-sulfur interaction, takes place in com- 7 parison with a similar test using the same motor oil but containing no bromoxylenes.

In another run employing the same oil composition, the same fuel is used with the exception that 1.5 stoichiometrical equivalents of mixed mono-bromo-xylenes are used in place of the ethylene halides as scavenging agent to obtain additional decreases in ORI during operation of the engine.

The halogenated hydrocarbons incorporated in the lubricating oils of the present invention are preferably those that do not volatilize to any appreciable extent at ordinary temperatures, and they preferably have volatility characteristics similar to those of the TEL in the fuel. They should be soluble in the lubricating oil into which they are incorporated in the concentration employed. They should also be combustible at the temperature prevailing in the aforesaid combustion chamhers in the presence of the fuel-air mixture introduced thereto. Preferably, these combustible halogenated hydrocarbons have a volatility at 120 F. in the range of about 0.2 to 6 mm. Hg, preferably about 0.5 to 5.0 mm. Hg.

The amount of these halogenated hydrocarbons added to the lubricating oil may be varied considerably, depending substantially on the specific compound used, the amount of sulfur and TEL present in the fuel, as well as other considerations. In the range of about 0.2 to 8% by weight of this material, based on the total lubricating oil composition, will generally suflice, with a preferred range being about 0.7 to 3% by weight. It is not essential to have a stoichiometric excess of the halogenated hydrocarbon in the lubricant based on the amount of TEL present in the fuel, although in some cases it may be desired to maintain a large stoichiometric excess of scavenger in this connection.

it is also preferred that the halogenated hydrocarbon be one that does not decompose under normal storage conditions and that does not form corrosive materials such as the hydrogen halides that are harmful to storage containers, fuel tanks and the like. Since higher boiling halogenated aliphatic hydrocarbons tend to form such corrosive materials, the halogenated aromatic hydrocarbonsare preferred in the practice of the present invention. In particular, the monoand poly-halogenated benzenes and alkyl benzenes are to be preferred, such as the bromoxylenes, dibromotoluenes, dichlorocumenes, dibromobenzene, their mixtures andthe like. Specifically preferred halogenated aliphatic and aromatic hydrocarbons are those having in the range of about 4 to 12 carbon atoms, especially 6 to 9 carbon atoms, and that contain no other inorganic or organic substituent groups. Such compounds include hexachlorobutadiene; 3,4-dichlorocumene; .l,2-dibromobenzene; l,2,4-trichlorobenzene; 2,4-dichlorotoluene; .mono-bromo-benzene; monobromo-toluene; dibromotoluenes, mixed mono-bromoxylenes; mono-bromo-mesitylene; mono-bromo-propylbenzene, etc.

Listed below are the vapor pressures of some of the suitable compounds useful in the compositions of the present invention.

Vapor pressure,

Halogenated hydrocarbon: mm. Hg at F.

Mixtures of these scavengers in various proportions may be employed in place of individual scavengers.

The lubricating oil base stocks used in the practice of the present invention may be of animal, vegetable, mineral or synthetic origin or mixtures of these that are compatible. Mineral oil base stocks are preferred. These are preferably distillates and residual stocks that have been refined by conventional procedures. These conventional refining procedures for removing the more aromatic portions, sulfur and other harmful constituents include treatment with mineral acids such as sulfuric acid; treatment with alkalis; solvent refining with various solvents such as phenol, furfural, sulfur dioxide, and the like; treatmentwith aluminum halides; extraction with silica gel; clay treatment; hydrogenation; desul-furization such as hydrofining; catalytic cracking, solvent dewaxing', etc.

Other suitable basestock constituents and blending agents include hydrogenated oils, synthetic oils resembling petroleum oils (polymerized olefins, synthesis products from the reaction of oxides ,of carbon with hydrogen or from hydrogenated coals, shale oil derivatives, 'et'c.), synthetic polyester and polyether-typ'e lubricants and the like. Such synthetic oils include di-Z-ethyl hexyl sebacate; di- C Oxo alcohol sebacate; complex esters of monohydroxy and dihydroxy alcohols and dibasic acids, polyethylene oxide-type synthetic oils with suitable terminal alcohol and ether groups, complex formal esters, etc.

The base stocks may have suitable viscosity, V.I., pour and other characteristics needed to formulate premium grade lubricants meeting SAE specifications ranging from 5 up to 40 grades and the like.

Particularly useful mineral oil base stocks for formulating motor oils are ones in which the base stock itself does not contribute substantially, to octane requirement increase. Such base stocks are taught in the aforementioned application, Ser. No. 375,158, filed in the names of L. E. Moody and A. H. Popkin on August 19, 1953. Such base stocks are those that have been treated to reamass move constituents that form resins when subjected to combustion under a smokeless flame and preferably have a resinification index as defined in said application below mg./5 g. These base stocks are conveniently prepared by solvent extraction of conventional mineral lubricating oils followed by dewaxing and distillation to form a relatively narrow boiling range fraction boiling below about 600 F. at 10 mm. absolute pressure, preferably in the range of about 300 to 550 F. at this pressure.

Other suitable base stocks are formed by solvent extraction and dewaxing if desired of a catalytically cracked cyclic stock as described in US. Serial No. 379,053, filed in the name of C. H. Holder et al. on September 8, 1953, the disclosures of which are incorporated herein by reference. V

The additive component s, other than the above described halogenated hydrocarbons, useful in the practice of the present invention to formulate the finished lubricants, maybeselected from any of the conventional addition agents needed to improve specific characteristics of the oil. I g

vOne of the more important additive materials to be used with the base stock of the present invention is a viscosity index improver. The finished lubricating oil for automotive use should have a high viscosity index; A suitable viscosity index improver as well as thickening agent is a high molecular Weight polymerized olefin, such as polymerized C to C olefins. For example, polymerized butenes and preferably polymerized isobutene having a, molecular weight in the range of about 5000 to 50,000, preferably about 10,000 to 25,000, are useful. These additives are especially suitable for increasing the viscosity of light neutral oils and other light distillates. For example, oils having S.U.S. viscosities below about 40 at 210 F. may be'incre'ased to higher viscosity oils such as those having viscosities above about 45 S.U.S. at 210 F., by the use of these V.I. improving thickening agents. In order to'increase viscosity and to improve viscosity index of the finished lubricant by as much as 10 to 70 units, it is generally desired to employ in the range of about 0.5 to 30.0' weight percent, preferably 1 to of the polyolefin based on the finished lubricating oil. Other viscosity index improvers include the polymethacrylate esters, fumarate-vinyl acetate copolymers, polyalk-ylstyrenes, and the like. Finished lubricants containing a mixtureof polyolefins and polyesters may be formulated. Thus from 3 to 10% of polybutene and '1 to 3% of a polyester may be used.

Another important additive to be employed in the finished lubricating oil of the present invention consists of at least one detergencyimproving additive. These agents will help maintain oil insoluble oxidation products and the like suspended injthe oil and will in general improve engine cleanliness. V

A wide variety of detergency improvers may be employed. One class of additives preferred for this use consists of the phosphorus and sulfur-containing hydrocarbons prepared by treatment of "a hydrocarbon with'a sulfide of phosphorus or a combination of the elements phosphorus and sulfur. These reaction products are well known to the art. h

As a general rule, the desire hydrocarbon, such as a paraffin, an olefin, a naphthene, 'an 'aromatic,a tepene, hydrocarbon resins, high molecular weight polymerized olefins, lubricating oil distillates, and the like are treated with a sulfide of phosphorus using a ratio of about one mole of phosphorus sulfide for 1 to 10, preferably 2 to 5,

mols of hydrocarbon at atemperature in the range of about 275 to 550 F. The resulting reaction product may be used as such, but it is preferred to refine it further by treatment with a suitable agent such as by reaction with a basic reacting material orby reaction with an esterification agent. Suitable basic reacting materials include the alkali metal and alkaline earth metal oxides, carbonates, hydroxides, hydrides and the like, specifically, potassium, sodium, barium, and calcium compounds. Basic inorganic compounds of heavier metalsmay be used, such as those of molybdenum, tin, zinc, chromium, manganese, nickel and the like. 7

Suitable ashless agents include nitrogen bases such as ammonia, and organicnitrogen bases such as amines and amine derivatives, guanidines and their'derivatives, morpholine, pyridine, quinoline and like substances. Guanidine and. its derivatives are particularly useful, the symmetrical tri-substituted compounds, such as ,trialkyl triphenyl and trinaphthenyl guanidines and the like being.

useful. Other useful compounds include the biguanides, dicyandiamides, dicyandiamidines, hydrazines, ureas, 'thio; ureas, 'semicarbazides, thiosemicarbazides, maleate and furnarate esters,v aminoalcohols, acrylonitrile alcohols, vinyl esters, phenols,.olefins such as diisobutylene, and the like.

' Treatment of the phosphosulfurized hydrocarbon product with these an d other agents may be carried out at any suitable temperature,such as from about room temperature up to 400 F. or so, using sufficient treating agent at'least to 'partially neutralize, esterifyyor combine with the titratableacidityof thephosphosulfurized material. Completely neutralized materials are usually preferred.

The treating procedure may be variedin several different ways. For example, the acidic'phosphosulfurized hydrocarbon may be hydrolyzed by treatment with steam followed by treatment with the treating agent. The partially or completelyneutralized products may be,hydro-' lyzed by steam trfeatmentyor the neutralization and hydrolysis may be carried out simultaneously. Hydrolysis in general reduces sulfur content, particularly helping to remove unstable sulfur.

Other detergents that may be used in the practice of the present invention include metal. soaps, metal organic sulfonates such as hydrocarbon sulfonates, including metal salts of petroleum sulfonic acids, metal phenates, metal alklates, metal alkyl phenol sulfides such as barium tertoctyl phenol sulfide, phosphates,dithiophosphates and thiophosphites, metal xanthates and thioxanthates, mixtures of these and other agents, coneutralized mixed metal additives such as coneutralized petroleum sulfonates and phenolic compounds such as alkyl phenol sulfides, etc. Thesedetergent additives are employed in various amounts, from as low as about 0.5 up to 10.0 or 15.0% by weight, based on the total oil, depending on the eflicacy of the, particular detergent.

In order to minimize oxidation characteristics of the oilsof the present invention, it is generally desired to add a suitable anti-oxidant or hearing corrosion inhibitor additive. Some of the detergent additives listed above have anti-oxidant characteristics but inother casesthey may adversely affect this property of the lubricant. i Particularly ,useful additives in this respect are lower olefinic hydrocarbons,particularly terpene hydrocarbons, that have been treated with a s'ulfide of phosphorus or with a combination of sulfur and phosphorusby the aa aass es s ur des ribed share sweiiieallv Pr r d ditive is prepared by treating alpha pinene withphosphorus penta-sul fide. This product may be used in amounts in the range of about 0.05 to 2.0% by weight in the composition with beneficial elfects. Other anti-oxidants include metal dihydrocarbon dithiophosphates, such as zinc dialkyl dithiophosphates, phenols, such as alkyl phenols, bis-alkyl phenols and the like, phenol sulfides such as tert.-alkyl phenol sulfides, metal dithiocarbamates, pheuothiazine andits alkylated derivatives, sulfohalogenated olefins that have been dehalogenated by known means, such dii sobutylene treated with a sulfur chloride, followed by dchalogenation, sulfun'zed dipentenes, etc. Variouscombinationsof these and other well-known antioxidants andcorrosion inhibitors may be used. W W

The amount of anti-oxidant employed in the finished lubricant will depend to a large extent on the type of base stock and the types of other-improving agents added thereto. As a general rule, in the range of about 0.01 to 5.0% by weight based on the total composition, will suffice to minimize the deleterious effects of oxidation. 7

A pour depressant additive is preferably employed in small amounts in order to meet pour point specifications. This additive should be one that not only"reduces the pour point substantially when used in small concentrations but should also be relatively stable in this regard when it is subjected to alternate cycles of heating and cooling; such as occurs in field storage, i.e., have a good pour point stability. Such pour point depressants include the chlorinated wax naphthalene condensation products, various polymers and copolymers of unsaturated esters and the like. These additives are generallyused in rather small amounts, in the range of about 0.01 to 2.0 weight percent based on the total'cornposition.

Other agents than those that have been mentioned may also be present in the composition, such as dyes, oiliness agents, anti-rust agents, plasticizers and defoamers, extreme pressure agents and the like.

The finished oils containing th'e basc stocks of the present invention will include at least one of the above types of additives, although two, or more different types of additives are generally desirable to formulate compositions containing all of the requirements of modern high compression ratio engines Based on the total composition, the additives will usually constitute a minor amount, and generally will be present inamounts below about 25% by weight, preferably about 31o 20% by weight.

It is also preferred that the addition agents used in the oil compositions have reduced tendency to contribute to OR I. Such additives are disclosed in the above-mentioned Serial No. 375,138. It is preferred that the finished lubricating oil compositions of the present invention have resinification iudiexes below about 20 mg./ g., especially below 10 trig/5 g.

The gasolines to be used in the high compression ratio automotive engines a d the. like lubricated by the oils of the present inventionmay be any suitable high octane, essentially hydrocarbon gasoline such as one having ASTM Research octane number in the. range of about 75 to 100. In a preferred aspect of the present invention, however, the gasoline will have a reduced resinification index in comparison with conventional commercial fuels. It is particularly preferred that the gasoline be one that will contribute no more than about 5 octane requirement units, preferably below one unit, increase when used in combination with the preferred lubricating oils of the present invention.

Conventional hydrocarbon components may be used in formulating such gasolines. These components 1nclude straight run distillates from various types of crudes, alkylates prepared by the.alkylati on of olefins w th isoparaflins, high octane polymers prepared by the catalytic polymerization of lower molecular weight olefins, hydrormat P pared b hydrocarbon distillates to form high octane aromatic components, reformed gasoline fractions prepared from straight run gasolines using conventional platinum cata: lysts, metal oxide catalysts and the like, catalytic cracked naphthas prepared by cracking gas oils, residuals, etc., in the presence of metal oxide catalysts such as silicaalumina, silica magnesia, and the like, and various other types of components that are conventionally employed in gasolines. Such gasolines are usually formulated by mixing two or more of the above general types of components in order to form gasolines meeting octane number vapor pressure, stability, and other specifications.

It has generally been found of the various hydrocarbon compounds present in gasolines that paraffins, naphthenes and olefins will not contribute, substantially, to CM. Aromatic components, particularly those having a boiling point higher than toluene contribute substantially to octane requirement increase. Those boiling above about 300 F. are especially undesirable for this purpose. Therefore, it is preferred that the gasoline contain no more than 20% by weight of aromatic hydrocarbons boiling above about 300 F., and more especially less thanabout 20% by weight of aromatics boiling above about 250 F. l 7

Lead tetraethyl is used in most commercial gasolines in concentrations ranging from about 0.1 to 3.0 cc./ gallon in order to increase octane number. Lead scavenging agents such as ethylene dibromide and ethylene dichloride are present in such compositions.

As a general rule, the above commercial gasolines will contain in excess of about.0.02 weight percent sulfor such as up to about0.2 sulfur or even higher. This invention has particular application to operations of engines with gasolines containingrelatively high amounts of sulfur, although it is generally desired that the sulfor content of the gasoline be below about 0.2% by weight. v

Although the gasolines generally contain low boiling lead scavenging agents such as the ethylene dibromide and dichloride described above, they preferably contain a relatively high boiling lead scavenging agent such as the halogenated hydrocarbons mentioned above and used in compounding the oils of the present invention. Generally in excess of about 0.5, preferably above about 1.0 stoichiometrical equivalents of such agents, based on TEL, may be added to the fuel. They preferably have, as described above, .vaporpressures at F. of about 0.5 to 5.0 mm. Hg. The use of such higher boiling scavenging agents in fuels is taught in various US. Patents, including 2,496,983; 2,574,321; 2,479,900, etc

The gasoline fuel may also contain other addit on agents such as antioxidants, gum inhibitors, solvent OllS, rust inhibitors, metal deactivators, etc.

This invention has particular application to the operation of automotive engines and the like that have compression ratios above about 7:1, and is particularly applicable to those having higher compression ratlos, for example, 7.5 to 1 and as high as 12:1 or higher. Such engines are extremely susceptible to octane requirement increase as mentioned heretofore, especially when they are run under rather mild conditions such as stop and go city traffic, suburban driving at relatively low speeds, and the like. Under these conditions the combustion chamberis particularly susceptible to deposit formation from resinous forming constituents in the lubricant and/or fuel. However, the invention is not restricted to automotive engines but will apply generally to the operation of any relatively high compression engine of this type, such as those in motor boats, aircraft and the like where automotive-type engines are subject to a substantial amount of mild operation.

What is claimed is:

1. In the method of operating an internal combustion engine having a compression ratio above about 7:1 in

which an essentially hydrocarbon fuel composition containing tetraethyl lead fluid and sulfur components is introduced into the combustion chamber thereof under combustion conditions, and in which a lubricating oil contacts the parts of said combustion chamber subject to friction, the improvement comprising the minimizing of octane requirement increase in the engine by introducing into said combustion chamber a lubricating oil composition boiling in the range of about 300 to 550 F. at a pressure of 10 mm. of Hg, having a resinification index not substantially above about 20 mg./5 g. and having dissolved therein 0.2 to 8% by weight of a halogenated aromatic hydrocarbon having 6 to 9 carbon atoms and a volatility at 120 F. in the range of about 0.2 to 6 mm. Hg.

2. The method according to claim 1 wherein said halogenated aromatic hydrocarbon comprises mixed monobromoxylenes.

3. The method according to claim 1 wherein said fuel contains at least about 0.02 wt. percent sulfur, in the range of about 0.1 to 3.0 cc. tetraethyl lead per gallon and at least about 0.5 stoic-biometric equivalents, based on the lead, of said halogenated aromatic hydrocarbon.

References Cited in the file of this patent UNITED STATES PATENTS OTHERYREFERENVCES Chlorine Compounds Added to Lubricants, Lincoln et al., I. and E. Chem, vol.' -28, pages 1191-1197, page 1194 pertinent. V v

S.A.-E. Journal, vol. 29, 1931, pages 215-222.

US. Dept. of Commerce, Tech. Paper, 500, 1931, I

page 16 pertinent.

=Ind. and Eng. Chem, vol. 45, No. 7, pages 1501- 

